Overheating on run stand

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4spdragtop

4spdragtop

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Not sure what the issue is but rebuilt 340 is overheating on run stand. Fired up today(2nd time on stand) to dial in timing and it's overheating to approx 110-120*C.
1st fireup was no stat. 2nd fireup I installed 180 stat. Not 100% sure on what timing is at yet, but approx 30* at approx 2300 rpm with va and carb both plugged.
Think it's timing??
Video of 2nd start
 
Want to get 4 full gallons of coolant into the block, heads and radiator.

If less than that you have an air lock.

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Steve a lean condition will cause it to over heat have you checked the air to fuel ratio or looked at the plugs? Not sure how much heat a lean condition would make but I’m sure it’s gonna run hotter
 
Helps to get the air out of the block and heads with the 1/8" hole drilled in the thermostat.

Screenshot_20231204-005730_Gallery.jpg



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1MeanA said:
Can you verify the temp is accurate?
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Thanks, yes, both gauge and temp gun are similar
George Jets said:
Want to get 4 full gallons of coolant into the block, heads and radiator.

If less than that you have an air lock.

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Thanks Casey, using water not coolant just in case of leaks etc(mess) I filled up thru the hose that I'm using to "jump" the fittings that feed heater core.
cudascott said:
Steve a lean condition will cause it to over heat have you checked the air to fuel ratio or looked at the plugs? Not sure how much heat a lean condition would make but I’m sure it’s gonna run hotter
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Thanks, I haven't checked plugs, BUT it is the same Eddy carb that was on 273. 1405 or 6
George Jets said:
Helps to get the air out of the block and heads with the 1/8" hole drilled in the thermostat.

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Thanks again Casey, I drilled a hole. I also verified in pot of water that it's functioning properly.
 
I agree with Cuda Scott spark plugs indicate A/F but also can read electrode build up on strap tip of spark plug if your timing is too Retarded or Advanced.
 
Thanks, yes, I haven't had a chance to chk plugs yet, but will do. I'm a newb with plugs, so I'll post pics of them over the next few days. Also plan on hooking vac gauge up, but didn't want to add that to the mix "just yet"
Speedy Pedi said:
I agree with Cuda Scott spark plugs indicate A/F but also can read electrode build up on strap tip of spark plug if your timing is too Retarded or Advanced.
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So no thermostat yielded no overheat and adding a 180 degree thermostat yielded overheating. That kind of points towards a faulty thermostat. I would recommend doing a few things.
1. Take out the thermostat.
2. Test the thermostat in a pan of water. It should "start" to open at 180 degrees.
3. Try to check for an airlock and drill a small hole in the thermostat like @George Jets suggested.
4. Run the engine without the thermostat and see if it overheats. If it doesn't, I'd try another thermostat.
5. If it does overheat, let it cool down completely and then:
a. Take the radiator cap off and start the engine. If the water pump is working properly, you should see water flowing
through the radiator. If not, maybe you need a new/better water pump.
b. Try playing with the timing.
c. Is the electric fan on the radiator big enough?
d. Was the block properly cleaned out in the water passages? You know what blockage there would do! Maybe a
thorough flushing of the block and heads would be in order.
That's about all I can think of. Good luck, Steve.
 
Thanks Mike, ran without stat, overheated.
2nd run installed 180 stat(drilled hole), still overheated.
Elec fans? I'm running normal 7 blade with shroud and oem ac rad.
Cap was off for part of 1st run, water was moving(no stat).
Stat was tested.
Block and heads don't need flushing, they are fresh heads. Block was bought from my machinist who's a Mopar guy and racer.
harrisonm said:
So no thermostat yielded no overheat and adding a 180 degree thermostat yielded overheating. That kind of points towards a faulty thermostat. I would recommend doing a few things.
1. Take out the thermostat.
2. Test the thermostat in a pan of water. It should "start" to open at 180 degrees.
3. Try to check for an airlock and drill a small hole in the thermostat like @George Jets suggested.
4. Run the engine without the thermostat and see if it overheats. If it doesn't, I'd try another thermostat.
5. If it does overheat, let it cool down completely and then:
a. Take the radiator cap off and start the engine. If the water pump is working properly, you should see water flowing
through the radiator. If not, maybe you need a new/better water pump.
b. Try playing with the timing.
c. Is the electric fan on the radiator big enough?
d. Was the block properly cleaned out in the water passages? You know what blockage there would do! Maybe a
thorough flushing of the block and heads would be in order.
That's about all I can think of. Good luck, Steve.
Click to expand...
 
If that's 30 degrees, yeah, it's the timing. Pull in like 45. Remember, you're on the stand and unloaded.
 
Thanks Rob, the timing #'s are a ballpark. Watching everything else, I didnt write the timing down. 45 seems like a lot with va unhooked?
I knew temps increased but couldn't remember if it was from advanced or retarded.
RustyRatRod said:
If that's 30 degrees, yeah, it's the timing. Pull in like 45. Remember, you're on the stand and unloaded.
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4spdragtop said:
Thanks Rob, the timing #'s are a ballpark. Watching everything else, I didnt the right timing down. 45 seems like a lot with va unhooked?
I knew temps increased but couldn't remember if it was from advanced or retarded.
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It is a lot. It's not under load! You need a lot so it won't run hot. I'd pull in anywhere from 36-45 at about 3000 RPM.
 
harrisonm said:
Wow, this is a head scratcher!
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No it's not. He doesn't have enough timing. That's probably THE biggest mistake made when breaking in an engine. With timing too far retarded, the mixture is igniting too late and still burning coming out of the exhaust. That will heat the engine up real quick. It's also very apparent on a new engine, because they are tight and have more resistance to running, which builds up even more heat. The best thing to do is, as SOON as it fires off, run it up to about 3000 RPM and pull in AT LEAST 35-36 degrees and more won't hurt a thing, since it's under ZERO load.
 
Agree with RRR. More timing on an unloaded engine. Engine is NOT driving the car, just itself.

Other thoughts:
- there will always be some air trapped in the cooling system of new engines. You have to run the engine, let the engine cool, to push the air out. This may take 2-3 cycles. The engine may run a few degrees hotter until all the air is out.
- if all new pistons, rings etc, it WILL run a little hotter.
- unless you have a special water pump that has NO bypass, there is no need to drill the stat, which will cause longer warm up time & no other benefit.
 
If the engine bearing clearances were set to factory spec 160 will exacerbate a tight new engine and temp.

I have heard of overheating due to ring gap being too tight.

If it overheats without a thermostat and with a thermostat it's not the thermostat.
 
I agree with RRR . That was my first thought. Advancing the timing is free and easy . Start there first.
 
RustyRatRod said:
No it's not. He doesn't have enough timing. That's probably THE biggest mistake made when breaking in an engine. With timing too far retarded, the mixture is igniting too late and still burning coming out of the exhaust. That will heat the engine up real quick. It's also very apparent on a new engine, because they are tight and have more resistance to running, which builds up even more heat. The best thing to do is, as SOON as it fires off, run it up to about 3000 RPM and pull in AT LEAST 35-36 degrees and more won't hurt a thing, since it's under ZERO load.
Click to expand...

Yup
 
To follow up reading plugs this a video that explains it. BTW I use a metal cutting small hole saw to separate spark plug by removing drill bit placing over porcelain tip.
 
Now would be a good time to shoot top/bottom rad fitting temps, then start adding timing and watch engine hose temps come down .
jmo
 
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